1. Field of the Invention
This invention relates to an integral multilayer analytical element for analysis of an analyte in an aqueous liquid sample. More particularly, this invention relates to an integral multilayer analytical element for analysis of an analyte in a liquid sample, such as a biological body fluid including blood (whole blood, blood plasma, blood serum), cerebrospinal fluid, lymph, saliva and urine, being dry-operative and useful for diagnosis in clinical field.
2. Description of the Prior Art
Integral multilayer analytical element is a form of dry-type analytical element being dry-operative and comprises a transparent support, a water-absorptive reagent layer containing a dye-forming reaction reagent and a hydrophilic polymer binder disposed thereon and a porous spreading layer disposed as the topmost layer. Various intergral multilayer analytical elements have been developed now.
The spreading layer has a metering action to spread an aqueous liquid sample spotted on the upper surface (the side far from the transparent support) thereof in lateral directions (the planar directions along the spreading layer) without uneven distribution of any component in the sample and to supply the sample to a water-absorptive reagent layer containing a hydrophilic polymer binder or a water absorption layer containing a hydrophilic polymer binder at a substantially fixed amount per unit area. The aqueous liquid sample includes biological body fluid, such as blood (whole blood, blood plasma, blood serum), lymph, saliva, cerebrospinal fluid, vaginal fluid or urine, drinking water, liquor, river water and industrial effluent. As the porous spreading layer, there are fibrous porous spreading layers, such as woven fabric spreading layers disclosed in U.S. Pat. No. 4,292,272 and GB 2,087,074A, knitted fabric spreading layers disclosed in EP 0,162,302A, the spreading layers composed of a paper containing fibrous pulp of an organic polymer disclosed in Japanese Patent KOKAI No. 57-148250 and the spreading layers formed by coating a suspension of fiber and hydrophilic polymer disclosed in U.S. Pat. No. 4,594,224, and nonfibrous porous spreading layers, such as membrane filter layers (blushed polymer layers) disclosed in U.S. Pat. No. 3,992,158 and continuous microspaces-containing isotropic porous layers (three dimensional lattice bead structure layer) where polymer particulates are joined so as to contact with each other at a point by using a polymer adhesive disclosed in U.S. Pat. No. 4,258,001.
Another form of dry-type analytical element being dry-operative is disclosed in DE 3,424,355A. The dry-type analytical element is a multilayer analytical element composed of a light-reflective or opaque support, a reagent layer containing a dye-forming reagent and a hydrophilic polymer binder to dissolve or solate by absorbing water and a porous registration layer disposed in this order. The porous registration layer may be composed of a similar material to the aforementioned spreading layer, and the spreading layer mentioned hereafter includes the porous registration layer unless other wise especially noted.
Among various spreading layers, woven fabric spreading layers and knitted fabric spreading layers (fabric spreading layer) can spread blood sample irrespective of whole blood, blood plasma or blood serum well, and they are excellent in the facility in the production of multilayer analytical element, the strength of the element and the like.
It is preferred that the spreading layer spreads the water in an aqueous liquid sample substantially without absorption, and therefore, the preferable fibers composing the fabric spreading layer are hydrophobic organic polymer fibers. However, in the multilayer analytical element where the fabric composed of hydrophobic organic polymer fiber is laminated onto a hydrophilic reagent layer through a thin gelatin binding layer like described in U.S. Pat. No. 4,292,272 or EP 0,162,302A, the adhesive strength of the spreading layer was insufficient. As a result, the spreading accuracy was inferior, and the analytical accuracy was insufficient.
In order to solve this problem, when the fabric was treated with glow discharge or corona discharge disclosed in GB 2,087,074A or glow discharge plasma treatment disclosed in Japanese Patent KOKOKU No. 59-11709, the adhesive strength was strengthened. As a result, the binding between the spreading layer and the reagent layer or the binding layer was made uniform, and the spreading accuracy was improved. However, another problem happened that undesirable interaction between a reagent component happened. That is, in the reagent layer in contact with the fabric spreading layer treated with glow discharge, corona discharge or plasma irradiation, when a diazonium salt was incorporated, the diazonium salt was decomposed, and the analytical accuracy became worse with the passage of storage time. While, when a tetrazolium salt was incorporated, the tetrazolium salt was reduced to produce a formazan dye. As a result, deviation of the analytical result occurred due to the irregular elevation of the base line of background, and the analytical accuracy became worse with the passage of storage time. Therefore, it was desired to develop a fabric spreading layer composed of a hydrophobic organic polymer fiber where the undesirable interaction between the reagent component and the degradation of the analytical accuracy with the storage time due to the interaction are removed, and the binding strength is sufficient.